Absorbent articles are well known in the art. Particularly sanitary napkins of all kinds of designs are well documented. Although the use of unitary cores is known in the art of disposable absorbent articles and has been disclosed previously such articles have not been successful or technically satisfactory as evidenced by the lack of commercially available embodiments.
The word “unitary” as used herein refers to a single structure, which despite potential internal variations of physical and/or chemical characteristics is provided such that it cannot be separated into individual layers. Such unitary structures are well known in the art and often referred to also as substrates. However, absorbent cores in disposable absorbent articles have been provided from a number of layers or associated with a multi-layer structure as the topsheet. In this context it is pointed out that a construction in which a topsheet with a second underlying layer, (at least in the region where liquid is usually deposited onto the article), referred to as secondary topsheet or distribution layer, is provided on top of a unitary absorbent structure, is excluded from the definition of the absorbent articles according to the present invention. Also structures made from a number of layers, which are joined to each other by macroscopic mechanical or adhesive means, are well know and not uncommon in the practical embodiments of absorbent articles available to consumers. Such structures, however, are also not considered unitary in the sense of the present invention since they are formed from individual layers that, albeit sometimes with difficulty, can be separated from each other again.
A unitary fluid acquisition, storage and wicking material is disclosed for example in WO 0074620 in which fibrous absorbent structures having separate strata or thickness regions for fluid acquisition storage and distribution are disclosed.
This disclosure, however, suffers from the design of an acquisition, storage and distribution layer system, which simply resembles the designs obtainable by a combination of layers. The fact that these layers are laid down in a single process, preferably as an air laid process, does not change the deficiencies originally found in the multi-layered constructions widely used in commercial article with the exception that the liquid communication between the layers is improved. The present application, however, also improves the ability of such unitary structures to mask stains visible on the topsheet side of an absorbent article, besides providing excellent liquid communication characteristics between the differing layers or strata.
The present invention also is particularly directed to the absorbent article employing unitary absorbent cores in such a way that no additional layers between the unitary topsheet and the unitary absorbent core is provided at least in the region where liquid is deposited during usual use. It is therefore an advantage of the present invention that a lay down of three layers, a topsheet, a unitary absorbent core and a backsheet is capable of providing the full and improved functionality of absorbent articles and thereby reduces manufacturing complexity for such articles. Within the various aspects of manufacturing complexity it should be noted that the simplification in raw material procurement, raw material delivery to a production facility and simplification of combining the raw materials to a finished absorbent article is much simplified with the absorbent article design according to the present invention.